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In 1999, I wrote of my first visit to Japan to study bonsai in a series of articles for The Journal. Again in 2002, I was fortunate to arrange a leave from work to embark on another visit to Japan. The two-month trip started in January with an eighteen-day tour in China and ended in March with an eighteen-day tour followed by three weeks of bonsai studies in Japan. While there were several cultural interests to enjoy, penjing in China and bonsai in Japan were a focus of the trip. In China I visited several gardens and culturally and historically significant places that allowed me to see many penjing which impressed upon me the widespread appreciation of this art form. One of the highlights in China was a visit to Hong Yuan (Red Garden) in Yangzhou where penjing master and internationally known artist, Mr. Zhao Qingquan "Brook," works his magic. At the end of our travels through China and Japan, I returned to Mr. Nakamura's Shonan School of Bonsai in Yokohama. The classes took place in March, a little more than a month later than my studies in 1999. The scheduling of the session in early spring allowed me to study in more detail another important aspect of bonsai...repotting. In addition to repotting, I learned about pruning, pinching, watering, fertilizing techniques and after care. Importance of Repotting Repotting bonsai is not simply a matter of placing a tree in a container and then filling in soil. Mr. Nakamura pointed out that, "It is not just repotting...it is very important." Repotting involves many decisions that affect the quality and health of the tree: securing the tree in the pot with wire, the use of well draining soils, and knowing the proper container size in terms of keeping the tree healthy. Other horticultural considerations include the balance of pruning both roots and branches, and the discovery of disease and insect problems in the soil that are uncovered by repotting, i.e. root galls, root-eating insect larva, etc. Many design decisions are executed while repotting such as placing the tree in the pot to show its best front, angle, soil depth and location inside the container. The tree's stage of development and how one shapes its progress is determined while repotting. I hope these and other considerations will become more apparent after learning from Mr. Nakamura in this and other articles. I have attempted to report accurately on what I have learned. Repotting Procedure During my twenty-one days with Mr. Nakamura, I repotted eighty-seven trees. Even though each tree was different, there was a similar approach with some variation to deciduous and coniferous trees, and young, developing trees and older, developed trees. The usual repotting procedure was as follows: 1. Sometimes Mr. Nakamura would touch the soil around a tree, checking its stiffness, to determine what needed repotting. Once he had decided that a particular tree needed repotting, a number of pots were selected from which the best one was chosen. There can be a number of reasons for repotting such as the tree had not been repotted for many years and thus needed the roots pruned to reinvigorate them and the soil changed to replace compacted soil that limited air space. Other trees may need another pot type or size depending upon their development stage, i.e. moving from a large training pot to a bonsai pot (I will discuss pot selection later). 2. Under Mr. Nakamura's direction, I prepared the selected pot by cutting black plastic screens to fit over the drain holes. Two mm aluminum wire was used to attach the screens (see illustration - Mr. Nakamura says that that wire screen clip will not become loose). Then 2 mm wire for small and medium trees (or 2.5 mm aluminum wire for large trees) was inserted through the drain or wire holes for tying in the tree. After choosing the best front for the pot (the glaze or surface area may vary), longer wire tails were put to the front and short ones to the back so that when they were wired in, they could be twisted at the back. |
 "Wire length is determined by hole size but on average the length of wire cutters works well. The gap size between the two loops is determined by the pot hole diameter. Bend wire tails down at 90 degrees to the loops. Push wire clip through screen. Place over pot hole from the inside, pull tails with pliers and fold over against bottom tightly." |
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3. I removed the tree from the old container by cutting the anchoring wires that were used to stabilize the root ball and prevent root damage when last repotted (anchoring wires are necessary to prevent the breaking of new roots as they grow after repotting). The screens were then loosened because roots usually grow around and through the screen. A potting knife and/or sickle was used to loosen the root ball from around the perimeter of the pot. Sometimes a soft rubber mallet was used to gently tap around the pot top lip to loosen the tree from the pot without breaking it. Since some of Mr. Nakamura's trees were purchased from other people and had not been repotted for many years (some as long as ten years), these root balls were very entrenched in the container. 4. A potting knife was used to cut 1/3 of the bottom soil and accompanying roots off. 5. Vertical cuts were made using the same knife around the periphery of the tree. If a tree had particularly dense, matted roots, Mr. Nakamura cut wedges of roots out to free up the surrounding roots to remove the old soil. Cutting through thick roots was avoided until the root system was cleaned so that an accurate assessment could be made. Heavy roots were reduced or removed and small ones were encouraged to grow by pruning very little or not at all. 6. A root hook was used to rake out the roots from the inside out. Mr. Nakamura says it is important to remove the top layer of soil because it can prevent water from penetrating the root ball. Fertilizer and salt from watering can accumulate on top. |
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7. After using the root hook, the potting stick (a large wooden chopstick) was used to remove more soil and tease out the root ball.
8. Sharp pruners were used to cut off long dangling roots and those around the perimeter. At this time crossing roots were removed and heavy roots removed or reduced to improve the rootage appearance (the amount removed depended upon each tree's health and development). This left a smaller root ball with about 1/3 to 1/2 of its roots removed. Mr. Nakamura has two sets of pruning tools, those for root pruning and those for branch pruning. Root pruning tools are subject to more abuse from the soil. Mr. Nakamura sharpens his tools regularly. |
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9. For most deciduous and especially younger trees, Mr. Nakamura washed the roots in order to get a more accurate view of the roots. Roots rarely washed were those of coniferous and older deciduous trees. For trees that had been collected or grown in a field, the older, finer soil had to be removed or it would become saturated with water and rot the roots even if the surrounding granular bonsai soil was slightly dry. 10. A layer of large sized Akadama soil (a granular clay-like Japanese bonsai soil) was placed in the bottom of the pot if it was deep enough, otherwise only medium sized soil was used at the bottom. To the Akadama soil, Mr. Nakamura added a 1/4 inch size light weight stone that holds water and air: 80% Akadama and 20% stone for coniferous trees and 90% Akadama and 10% stone for deciduous trees. Mr. Nakamura said that the stone made the trees work harder and thus develop rougher bark. For older more refined trees Mr. Nakamura used straight Akadama and sometimes put a fine dressing of Akadama on top after all repotting was completed but before watering. 11. The tree was placed in the pot at the right attitude and position by first building a small hill of soil under the tree, then twisting and pushing it downward. With the tree in position, the tie wires were tightened, sometimes using rubber pads or pieces of drain hole screening to protect the roots from the crushing affect of the tie wires. I found this step quite tricky because the soil, which was quite granular, could collapse under the tree resulting in the tree being too low in the pot or, if using too much soil, too high. Here the different stage of the tree's development came into play with the younger, developing tree placed deeper in the pot to increase its vigour. For a tree ready for exhibit, the surface roots need to be exposed, therefore these trees need to sit higher. 12. More soil was added and worked in among the roots with a potting stick while lightly pressing the soil down with the finger tips. After a certain amount of time, the soil will become stiffer. Tapping around the sides with a soft rubber mallet helps to settle and equalize soil density and level. The soil level should be 1 cm below the lip of the pot. This allows water to pool when watering and prevents soil from being easily washed away. This space also allows for the placement of moss. 13. The tree was re-checked to verify its correct position. The wires were tightened as necessary which might be the case after the soil settled. 14. The tree was then watered with a fine spray nozzle until the water ran clear. 15. After I had completed the repotting, I placed the tree in full sun. All of Mr. Nakamura's trees were placed in full or partial sun except the more expensive ones and some of the pines that had been repotted a little early. These trees were protected in a greenhouse or unheated building since the nights could drop near or below 0 degrees Celsius. Mr. Nakamura pointed out that it is photosynthesis that develops the roots. He told me about a valuable azalea that died because it was put in shady conditions instead of sun. The trees should also be kept away from windy conditions. The repotting steps outlined above are used by Mr. Nakamura, a bonsai master. As an amateur, I am more cautious. In southern Ontario where spring can get hot quickly, I believe that sunny conditions, especially morning sun, is OK for deciduous trees. However, I think that more caution should be exercised for evergreens. Trees have to be watched closely because they will tell you about any problem, although with conifers like pines, they may be dead before you notice. After I had repotted a couple of pines last year, I put them in shade for a week or so and then gradually moved them to semi-shaded conditions. When I noticed that the candles were not elongating and the needles were not greening up like they should, I took them out of the sun for several weeks and then re-introduced them to the sun and they survived. I think another consideration is the longer time trees in Japan have been growing in pots and adapting to those conditions whereas our older bonsai are those that have often been collected and have not yet developed a multi-rooted system. Mr. Nakamura said to only water newly potted bonsai when the top soil becomes dry because with regular watering, the fewer roots won't absorb all of the water which can then lead to root rot. I mist frequently. Advanced Repotting Techniques Among some of the amazing work I saw Mr. Nakamura perform were advanced repotting techniques. One was the chiselling out of heavy roots at the base of several large acer palmatums (maple). Another was repotting a pinus parviflora (Japanese white pine) clump. The photos will help illustrate these techniques, and repotting in general. Acer palmatum root chiselling: Mr. Nakamura said that it is important to reduce an overly strong root with its future appearance in mind. He noted that some people like a large heavy root base but he felt that it looked artificial. He used a curved chisel and a hammer to take large sections of the roots out on a beech and several maples, including one of his best trees. The cut was tapered away from the trunk at about a 45-degree angle. A wooden board under the tree protected both the tree and the chisel. Mr. Nakamura felt that it would take about ten years to heal. Cut paste was put on these large cuts. |
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Pinus parviflora five tree clump: Mr. Nakamura estimated that this tree had not been repotted for about ten years. It was growing out of the pot by one inch. There is an article on repotting two pines that were also long overdue for transplants in the recent issue of Bonsai Today #82. |
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